Radial compressors are known for example from EP 1 356 168 B1 or from EP 1 602 810 A1.
Such radial compressors are composed of a rotor or vane impeller which forms a compressor stage and which rotates about an axis of rotation and which has—with respect to the axis of rotation of the rotor—an axial inlet and a radial outlet. Gas to be compressed flows axially into the rotor of the compressor stage and is then diverted outward (radially, radial direction), wherein said gas exits the rotor at high speed.
Kinetic energy of the gas to be compressed which exits at high speed is then converted in a diffuser into potential energy in the form of pressure.
Such a diffuser is usually formed by two non-rotating rings which form an annular hollow chamber or an annular chamber, which annular chamber radially adjoins the rotor outlet, or which rings or annular walls/side surfaces adjoin the rotor outlet radially and are perpendicular to the axis of rotation or are at a highly obtuse angle with respect to said axis of rotation (radial annular chamber walls/radial side surfaces).
The gas exiting the rotor is conducted radially outward in said annular chamber between said two annular walls and passes to a collector.
Diffusers commonly have vanes, that is to say a blade arrangement, for diversion and improved control of the slowing of the flow.
It is also known that such radial compressors exhibit relatively high sound emissions or noise levels which constitute a (noise) disturbance in the surroundings of the radial compressor. Said sound emissions may furthermore also cause vibrations and structure-relevant malfunctions.
Dominant sound sources in a radial compressor are for example typically generated at the location of the vane impeller and of the diffuser inlet or any diffuser blades, owing to the high speed of the fluids flowing through said regions and owing to an interaction of rotor and stator components.
In particular, it is known here that radial compressors generate complex, transient, three-dimensional, rotating and/or pulsating pressure fields or sound fields at an outlet from the radial compressor (pressure side), for example at a pressure connection piece at said outlet, the sound waves of which pressure fields or sound fields propagate without disruption into the pipelines adjoining the pressure connection piece.
Here, in addition to the said noise disturbances, vibrations and structure-relevant malfunctions, pipeline vibrations may also occur which may lead to damage to the pipelines to the point of failure of the radial compressor or of the superordinate system that has the radial compressor.
The damping of such complex, transient, three-dimensional, rotating and/or pulsating pressure fields or sound fields is technically difficult.
Taking this as a starting point, efficient sound damping measures are necessary for sound-emission-generating radial compressors of said type.
Various “external” measures for limiting sound emissions, such as housings or casings, are known. Said noise reduction techniques may be relatively expensive, in particular if they are marketed as an “aftermarket” add-on product.
Furthermore, “internal” silencers for limiting sound emissions in the case of radial compressors are known.
Silencers in general are devices for preventing sound emissions. It is possible to distinguish between various types of silencers which reduce a generated acoustic power on the basis of different mechanisms. A distinction is made, for example, between adsorption and reflection/resonator silencers.
An absorption silencer such as is known for example from EP 1 602 810 A1 for a radial compressor comprises porous (adsorption) material, generally mineral wool, glass wool or glass fiber, which partially absorbs acoustic energy, that is to say converts said acoustic energy into heat. By means of absorption, primarily upper frequencies of the sound medium are damped in the silencer.
Similar fillings of a corresponding hollow chamber are also proposed in DE 603 10 663 T2, DE 601 20769 T2 and US 2009/229280 A1. DE 601 14 484 T2 discloses a circumferential groove whose depth is enlarged to more than 1.5 times the axial width of the cut-out portion of the compressor wheel.
Absorption silencers have the disadvantage that they are generally unsuitable for high pressures, because—owing to the high pressures—large amounts of energy act on the absorption material, or large amounts of heat must be absorbed by the absorption material, which can lead to damage to the porous material, such as for example a disintegration of the absorption material.
Resonator silencers or reflection silencers, which utilize the principle of acoustic reflection, generally comprise for this purpose multiple cavities or chambers which are passed by the sound medium, wherein reflections occur. As the sound medium passes repeatedly by interior spaces of the chambers, a reduction of acoustic pressure peaks of various frequencies occurs. Said reflections are—in structural terms—generated by impact walls, cross-sectional widenings and narrowings. By means of reflection, it is possible for any desired frequencies of the sound medium to be damped in the silencer.
Such a resonator silencer, based on a Helmholtz resonator principle, for a radial compressor is known from EP 1 356 168 B1 or from EP 1 443 217 A2. In said radial compressor, the diffuser therein has an acoustic lining in the form of an area with numerous bores which act as Helmholtz resonators.
In addition to a radial compressor of said type, a further known form of radial turbomachine is a radial turbine.
Such a radial turbine, such as is known for example from DE 44 38 611 C1, is based on a reversal of the physical principle of a radial compressor, and is accordingly—with corresponding components to those in a radial compressor—traversed by flow in a flow direction opposite to that in said radial compressor.
In radial turbines, too, the described emission problems arise in a corresponding manner.
For example, dominant sound sources in a radial turbine are typically generated at the location of the vane impeller or of a turbine wheel (both also referred to hereinafter for short as “rotor”) and of a turbine guide ring, or any guide ring blades, positioned upstream of the turbine wheel.
Here, too, it is possible for complex, transient, three-dimensional, rotating and/or pulsating pressure fields or sound fields to be generated at a suction side, that is to say at an inlet into the radial turbine, for example at a suction connection piece at said inlet, the sound waves of which pressure fields or sound fields propagate without disruption into the pipelines connected upstream to the suction connection piece.
Taking this as a starting point, efficient sound damping measures are necessary here, too, for sound-emission-generating radial turbines of said type.